Radio signaling system employing machine-switching dial



RADIO SIGNALING SYSTEM EMPLO YIN G MACHINE SWITCHING DIAL 2 Sheets-Sheet 1 Fiied May 27. 1924 IN VEN TOR Z. uffmgmk fTTORNEy March 20, 1928.

M. L. ALMQUIST RADIO SIGNALING SYSTEM EMPLOYING MACHINE SWITCHING DIAL Filed May 27. 1924 2 Sheets-Sheet 2 IN VEN TO R J1 Z. 1122 yaw! ATTORNEY Patented Mar. 20, 1928.

warren srarss recast? PATENT @FFFEQE.

MILTON L. ALIVIQUIST, OF BROOKLYN, NEW YORK, ASSIGNOR 'I'O AMERICAN TELE- PHONE AND TELEGRAPH GOIll'tIEANY, A CORPORATION OF NEW YORK.

RADIO SIGNALING SYSTEM EMPLOYING MACHINE-SWITCHING DIAL.

Application filed May 27,

This invention relates to signaling circuits and more particularly to arrangements for transmitting selective signals over circuits employing carrier frequencies such, for enample, as multiplex carrier systems or radio signaling systems.

In systems employing high frequency currents as carriers of signals and particularly in the case of radio signaling systems, it is desirable to provide selective arrangements for transmitting ringing or other supervisory signals by means of code combinations. This is desirable not only to insure that the proper receiving stations will be selected and signaled, but also to prevent false operation of a signal at any stations by means of transient disturbances.

In accordance with the invention it is proposed to provide a signaling systenrof the type above described which will ut1hze as the code forming mechanism at the transmitting station the ordinary dial used in machine switching and which will preferably employ at the receiving station a selective switch of the type employed in machine switching. The invention. also comprises, among other things, the provision of a special selective circuit arrangement whereby the switch may be successively operated in response to successive groups of code impulses to establish the final signaling circuit at the receiving station. By this arrangement it is possible to assign each receiving station a number and by simply dialing the code numher, the desired receiving station will have its selective apparatus so operated as to actuate the signal at that station, while the other stations having different numbers will not have their signaling apparatus operated.

The invention may now be more fully understood from the following description when read in connection with the accompanying drawing, Figure 1 of which illustrates schi-nnatically the arrangement of the'apparatus embodying the invention as applied to a transmitting and a receiving station of a. radio signaling system, and Fig. 2 of which illustrates the circuit details of the selecting mechanism employed at the receiving station, and Figs. 2 and 2 of which show details of the switch mechanism.

Referring to Fig. 1, TL designates an ordinary telephone transmission line which 1924. Serial N0. 716,208.

is connected over the contacts of a relay 21 to radio transmitting apparatus, convention ally indicated at T. This apparatus may be of any type well known in the art whereby telephonic waves may be impressed upon the radio frequencies and transmitted from an antenna such as TA. For example, the apparatus may be of the type shown in United btates patent to H. A. Aftel,'No. 1,472,822, of November 6, 1923. In order to transmit a ringing signal through the radio transmitter, a dial D is provided, this dial being of the type commonly employed in connection with machine switching systems. A source of ringing current 20 is provided, having a frequency, for example, of 135 cycles, and the contacts of the relay 21 are so arranged that whenever the relay is deenergized the radio transmitter is disconnected from the line TL and the ringing current connected to the transmitter for modulating the radio frequency in any well known manner. The circuit of the'relay 21 is normally closed through contacts of the dial D so that when the dial is operated the circuit of the relay 21 is successively opened a number of times corresponding to the particular digit dialed. This permits of the transmission of groups of 135 cycle oscillations corresponding in number to the number of pulses transmitted by the dial. The of? normal contact of the dial is arranged to connect ground to the starting lead of the ringing current source to set the generatorof said source into operation in a well known manner. See, for example, United States patent to C. S. Demarest, No. 1,317,155, of September 30, 1919.

The receiving apparatus comprises a receiving antenna BA with which is associated a radio receiving mechanism conventionally illustrated at B. This mechanism may be of any well known type, by which the modulated radio frequency is translated into signaling currents of the type originally im pressed upon the radio transmitter at the transmitting station. See the receiving apparatus of United States patent to Atfel, above referred to. The successive groups of 135 cycle current are accordingly detected by the apparatus R at the receiving station and impressed upon the circuit of an alternating current relay 22, the circuit of this corresponds to a relay being tuned to 135 cycles. Each time a group of 135 cycle oscillations is received the relay 22 operates to maintain the relay 23 engerized during the continuance of the group. Relay 23 will accordingly receive pulses corresponding to those transmitted by the dial D and will transmit these pulses over the circuit 2d to the selecting apparatus conventionally indicated at 25. If the code signal transmitted corresponds to that assigned to the particular receiving station illustrated, the selector apparatus is so actuated'as to complete a circuit for the hell or other signaling device 26.

The details of the selector circuit are as shown in Fig. 2. The selector switch proper consists of three banks of contacts A, B and C, over which wipers may be advanced step by step under the control. of a stepping magnet S. Each bank of contacts consists of two groups of 11 contacts each, one of which normal position of the switch and is designated N, and of which the other contacts are numbered in regular order, beginning with l and ending with 0. The two groups of 11 contacts each are exactly alike and the individual contacts of each group are sintiilarly connected to con trolled circuits so that each group of 11 contacts constitutes, in effect, a complete switching unit. each bank of contacts has two wipers associated therewith, one of which will normally rest upon one of the N contacts of the bank. The switches are so arranged that they can be advanced step by step in one direction only, and as one of the wipers passes over the successive contacts of the first group until it comes upon the N contact of the next group it has completed one cycle of operations. As it is then advanced step by stepto the last N contact, it

the normal contacts designated N.

completes a second cycle of operations. At this time the second wiper rests upon the first N contact and as the switch is further to the last N contact it completes a fourth cycle. Consequently, by means of two groups of contacts and two wipers for each bank each switch may be made to pass through four similar cycles by continuous step by step rotation, and each cycle will, to all intents and purposes, correspond to one complete operation of single switch having 11 contacts arranged in one complete circular bank. lVherever, in the following description and in the appended cl aims, referenceis made to the normal position of the switch it will be understood that by this is meant any setting of the switch whereby either one of the wipers rests on any one of The wipers on banks A and B are such as not response to a proper received code combination successive translating circuits are operated whereby the signal 26 is finally actuated. In theicase ofthe circuit illustrated, the selector apparatus is arranged to properlyre spond to dialing'of the number 1687; Of

these digits, the first digit serves merely to restore all of the apparatus of the various selectors at the several stations to normal. and the lastthree digits constitute the actual selecting code for causing the actuation of the signal 26 at the desired station. Therefore, in the circuit illustrated, contacts numbered 3, 6 and 7 only are live contacts.

The contacts of banks A and C are so wired as to advance the selector switch to normal aftcrhaving been advanced froma normal position in response to a dialing operation. All of the odd numbered con tacts of the bank A except those contacts corresponding to thedigits of the code nu1nber of the particular station involved are wired to a relay 2, while all of the even numbered contacts except thoseinvolved in the digits of the code number of the particular station are wired to the relay 3. Consequently, if the switch at any station is advanced to a position corresponding to adigit not involved in the code number of the particular station, one of the relays2 or 3 will be released to control a self-interrupting circuit for the stepping magnet S, so that the switch willbe advanced to the next succeeding normal contact. The automatically interrupting circuit ofthe magnet S is also controlled by the contacts ofthe bank C and the N contacts of the bank C are so wired as to interrupt the automatic stepping operationsov that the switch is brought to rest on a normal contact. In the case of the switch at a station whose number being dialed, each time the switch is successively advanced to acontact corresponding to oneof the digits of its code number, a translating operation is performed and a selecting circuit completed. The further advance of the switch to the succeeding normal contact is then made under the control of the contacts of the bank C and the selected translating circuit, while the contacts of the bank A perform no function in advancing the switch to normal. i

Further details of the apparatus may now be understood from a. description of the operation, which is as follows: Let us'assume that the dial D of Fig. 1 is actuated to trans mit the number 1637. Successive groups of code impulses will be transmitted to the neeasv'f relay 21 so that for each impulse of a group received by the antenna RA and impressed upon the radio receiver R, which operates to detect groups of 135 cycle oscillations corresponding to' the code impulses transmitted. Each group of 135 cycle oscillations actuates the relay 22 to transmit one pulse through the relay 23. As successive groups of pulses are received, relay 23 transmits the pulses to the relay 1.v Upon receiving thev single pulse corresponding to thedigit 1, relay 1 closes a circuit of the stepping magnet S and advances the selector switch from its normal position to its first contact. This connects ground to one terminal of the slow release relay 2, thereby short-circuiting its winding' After a brief interval, the slow release relay 2 is deenergized. In this connection it should be noted that the relays 2 and 3 are made slow releasing so that when the wiper of the switch momentarily passes over one of the contacts connecting ground to the winding of one of its relays in being advanced to a further contact, the corresponding relay will not be released, but when the wiper is permitted to rest on such a contact for a short interval of time the relay will be deenergized to advance the switch to the next normal position in the manner about to be described.

The release of the relay 2 completes the circuit of relay 7, which upon being energized opens, at its lower contact, the circuit of any of the selecting relays 11, 14 or 17 which may have been previously energized 'and locked up. This restores the selecting circuits to normal and this operation occurs at all of the selectors of all of the stations so that each of the selectors is now ready to receive the next three digits of the code number transmitted. Relay 7, at its upper front contact, completes a circuit. for the relay 8,,whicl1 is locked up over the upper back contact of relay 9. Relay 8, at its lower front contact, completes a self-interrupting circuit for the stepping magnet S, from battery, through the winding of said magnet, and over its interrupting armature, thence over the contact of relay 8 and over the first contact of switch bank C to ground. This self-interrupting circuit is held closed over the successive contacts of the bank C until the succeeding normal contact N is reached. The wipers on bank C are such as to bridge the contact-s between successive points so as not to cause any interruptions when passing from one contact to another. The stepping circuit is now interrupted at contact N so that the switch comes to rest and a circuit is completed from ground, over the N contact, and through the winding of the relay 9. Relay 9, upon being energized, opens the locking circuit of the relay 8, which is at once released, the stepping circuit being now held open at the lower contact of the relay 8. All of the switches atall of the stations now have one of their wipers resting on one of their normal contacts.

Upon receiving the six pulses corresponding to digit 6, the stepping relay S advances the switch six steps so that the wipers rest upon the contacts numbered 6. In the case of the circuit illustrated in Fig. 2, ground will now be connected over the sixth contact of the bank B and over the upper back contact of relay 12 to one terminal of the winding of the slow-release relay 4, thereby shortcircuiting said relay. After a brief interval, relay t is released and closes the circuit of relay 10. Relay 10, at its lower front contact, operates the selecting relay 11 which locks up over its lower contact. At its upper front contact, relay 10 completes a circuit,

to relay 11, upper front contact of relay 10,'

from ground, over the upper front contact of and through the winding of, relay 8 to battery. Relay 8 is accordingly energized and locked up as before. At its lower front contact, relay 8 completes a self-interrupting circuit over one of the wipers of the bank 0 so that the stepping magnet S advances the switch to the next normal position N. The self-interrupting circuit is now open so that the switch comes to rest and the relay 9 is energized'to unlock relay 8 as before. As soon as the wiper of bank B leaves the sixth contact, the short circuit is removed from relay 4, so that said relay is again energized and opens the circuit of relay 10. A circuit is then completed for relay 12, from ground, over the upper front contact of locked up relay 11, over the upper back contact of relay 10, through the winding of relay 12 to battery.

All of the selectors at stations whose second digit is 6 will be operated in. a manner similar to that above described. In the case of the selectors at stations none of whose digits are 6, however, the sixth contact of the A bank will be wired to a relay corresponding to relay 3, so that said relay will be short-circuited and will release its ar1nature to complete the circuit of a relay corresponding to relay 7. In the case of stations whose third or fourth digit is 6, the sixth contact of B bank will be connected to a relay corresponding to relay 2 of Fig. 2

through the upper back contact of relay 15 the selector switches ofthe system are now.- -1n normal posit on-readyto receive the succeeding digit, .whichin the case assumed is 3.

Upon receiving; {the three, impulses correspondi-ngto the third. digit 3, the stepping magnet S advances the selector switch three steps, thereby'connecting ground over one of thewipers theiB bank and the third con.- tact thereof, and over the upper back contact of relay and lower front contact of relay 12 to a terminalof the slow-release relay 5. Thewinding of relay 5 is accordinglyshortcircuited. and upon releasing its armature V completes a circuit ofv relay13. Relay 13,

ati its, lower front contact, completes a ir-. 'cuitof relay 14, which is at once looked up. At its upper front contact, relay 14 completes av circuit from, ground, ,over the upper front, contact of relay'13'aud through the windingof relay 8 to battery. Relay 8 operates'as beforeitoadvance' the selector switch. to the succeeding normal POSIUOH where it will. con elto. rest. Assoon as the wiper ot' theibankB leayes the third contact, the short circuit is reinove'dl fr orn relay'5, so that said relay is again,.enei'gized'and opens the circuit.v of relayj13. A 'c'ircuitis then completed for the relay '15, from ground, over the upper. front contact of locked up relay 14,over 'the upper'ba'ck contact of relay 13, through 'the windingof relay 15 to battery.

The operation above described takes place at all stations, the. first three digits ot'whose numbers are 163. At stations no'neofqwhose digits is3 ,'a relay correspondijng to relay 2 willi be short-circuitedby the third "contact of the A bank connecting toground over one of the wipers ofsaid bank. In'the case of selectors, whosethird' digit is3'but whose second'digit isnot 6, or'wh'ose fourth'digit' is 3', the third contact of B'bankwill be connected to' a relay corresponding to relay of Fig. 2 through 'the upperback 'contact', of relay '15. and the lower back contact of relay 12, or through the lower back contact Iof relay l5, 'sothat relay 2 will be short circuited. 'Relay 2, on beingsliort cireuited releases andjenergizes a relaycorresponding to 7 whichfin turn energii'es andflo'cks up a relay corresponding to 8, so that the selector switches at suchfstat'ions are ad- Vancedto the next normal position. Relay 7 alsofremoves'battery from relay-14, causing it to release if locked up. At stations whose second digit 3', relay 4 w'iillreleasc, operating relay 10, and locking "up relay 11, 'and' I causing 'the' selector to advance to the next normal position. Nyaspreviously described \Vhen the setrof impulses corresponding to digit 7 is received, the stepping magnet Sadvances the selector switch to its seventh contact, so that ground is connected over the wiper and seventh contact of theF-bank B, over the lower front contact of relay 15 to the terminal of slow-release relay 6. Slowrelease relay 16. Relay16 in turn energizes andlocksup relay 17. "Relay l'f completes a'circuitfrom ground, over its, upper front contact, and over the upper"front contact of relay 16, through the winding of relay 8-to battery. RelayS is locked upaand advances the switch to, its next normal position, as already described. As the switch is advanced-the wiperleaves the seventh contact of the bank B so that the short circuit is removed from the-winding of relay 6. Relay'6, upon being, energized, opens the circuit of relay 16, thereby releasing said relay and completing a signaling circuit as follows: -Fronr ground, overfthe upper frontcon'tact-ot relay 17, u 'iper back contact of relay 16, andthrough thesignal 26' to battery. A parallel circuit is also established through. the winding of the slow-operating relay 18 so that after a given time therelay 1.8 will open the looking circuit 'of relaysll, 14 and 17, thus restoring these relays to" normal. The release of'relay 17 opens the circuit just traced for the signal'26 so that the signal n iw ceases. If desired, the operation of the signalfim ay be stopped at any time by merely opening "the contactof the key K.

Stations, the first three digits of whose code 1'63,but having othcr numbers than 7' forftheir last digit will have their selectors advanced'to the seventh point but-at suchstations a relay corresponding to relay 20f Fig. 21 will be connected either to contact 7 on the A'bank, or through lead 30 and the lower back contact of relays 12 or 15 to contact 7 011 B bank and will thereforebe short-circuited, so that tlieselect'ors at, such'stations will be restored tonormal; The selectors atother stations having 7 for one of their se'lective di'gits other than the first'will havetlieir selectors advanced to the seventh contact. Except in the case ofs'tationswhose second selective digit is 3, and'whose first selected digit is anumber other than 6, the relays corresponding to 12 and'15'of Fig. 2-at' such stations'will not. be energized. Consequently, a circuit will be completed from ground,over the seventh contact ofthe Bba'nk at 'such'stations, and over thelower back contact of the relay corresponding to '15, or the upper back contact of relay 15 andthe lower back contact of relay"12"at' suchstations, and thence over conductor 30"to a'terminal of the winding of the relay corresponding to 2, which will 6 is thus short-circuitedand uponreleasing completes a circuit for relay 7 This wvill result in locking up the relays corresponding to 11 and 12 at such stations and also will result in the energization of the relay corresponding to 8, which restores the selector switches at these stations to normal. Relays corresponding to 11 and 12 will be unloeked and restored to normal under the control of the relay corresponding to 2, when the digit 1 is dialed intransmitting the next code number.

Stations whose second selective digit is 7, and whose first selective digit is 3 will likewise have their selectors advanced to the seventh point in response to the dialing of the last selective digit of the code number of the station called. At such stations a circuit will be completed from ground, over their seventh contacts, and thence over the upper back contact of arelay corresponding to 15 and the lower front contact of a relay corresponding to 12 to a relay corresponding to 5.- This results'in a sequence of relay operations which results in relays 14 andv 15 being locked up and the selector being returned to its normal position as previously described. The relays 11, 12, 14 and 15 which are locked up will be released in responsetothe dialing of the digit 1 preceding the next code number. g

The above illustrations are suflicient to indicate that when any selector at any station is moved as normal, it will be advanced to its next normal'position in a manner similar to one'of the "ways already described, and'while some of the selecting relays may remain locked up at stations which are not called, the dialing of the digit 1 preceding the next selective code will restore any relays locked up so that all the apparatus at all of the stations will be in normal condition beforethe first selective digit of any code combination of three, selective digits is dialed. i 7

'It will be obvious that the general principles herein disclosed may be] embodied in many other organizations widely different from those. illustrated without departing from the spirit and scope of the appended claims. 7

What is claimed is: 1. In a signaling system, means for selectively signaling a desired station comprising meansfor transmitting the code number of the station in the form of successive digits, means at a receiving station for receiving the code number, a. selector switch at the receiving station controlled by said means, means to advance said selector switch oil normal in response to each digit, means to bring said selector to normal between digits, a signaling circuit, and means actuated to complete said circuit by successively advancing the selector switch in response only to each di it of the code of that station. v

2. In a signaling system, means for selectively signaling a desired station comprising means for transmitting the code numberof the station in the form of successive digits, means at a receiving station for receiving the vcode number, a selector switch at the receiving station cont-rolled by said means,

'means to advance said selector switch ofi normal in response to each digit, means to bring said selector to normal between digits, selecting relays, one corresponding to each selecting digit of the code number, means to successively operate the selecting relays in response to the successive operation of the selector switch, and a signaling circuit completed only upon. the successive operation of said relays in response to the code for the selected station.

. 3. In a signaling system, means for selecactuate one of said relays only it said digit is the first selective digit of the code number of that station, means whereby the successive actuation of the selector switch in response to additional digits will actuate the remaining selecting relays only when the digits receive correspond to the digits of the number'of the station, and a signaling cir- 'cuit controlledby said selecting relays.

4.111 a signaling system, a transmitting station-and a plurality or" receiving stations, means at the transmitting station for selectively signalinga desired receiving station comprising means for transmitting the code number of the station in the form of successive digits. means at the receiving stations for receiving the code number, a selector switch at each receiving station controlled by said means, means to advance said selector 0E normal in response to each digit,

ceived radio waves into ringing currents,

means to bring said selector switch to normal between digits, a plurality of selecting relays at each receiving station, one corresponding to each selective digit of a code number, means responsive to the first digit to bring the selector switches at all receiving stations and their associated apparatus to normal, means responsive to the second digitto actuate the selector switch at each receiving station and complete the circuit of the selecting relay there at only if the digit corresponds to a digit of the code number of the station, means to actuate the other selecting relays at each receiving station in response to the successive actuation of the selector switch at each station only when the selective digits actuating the switch corre 'spond to the remaining digits of the code number of the particular station, and means to complete a signaling circuit under the control of said selecting relays at the desired station;

5. In a radio telephone-system, means for selectively signaling a desired station comprising means for transmitting the code number of the station in the form of suc- 'cessive digits, a radio transmitter, means to apply ringing current to said radio transmitter in accordance with the dialed code, means at-a receiving station to translate remea'ns for translating the ringing currents into'the code number, a selector switch at the receiving station controlled by said means, means to advance said selectorswitch ofl normal in response to each digit, means to bring said selector switch to normal between digits, a signalingcircuit, and means actuated to complete said *circuit by successively advancing the selector switch in 'response only to each digit of the code ofthat station.

6. In a radio telephone system, means for selectively signaling a desired station COII1 ip'rising means for transmitting the code number of the station in the form of successive di its, 'a radio transmitter, means'to ap- -pl=y ringing current to said radio transmit- 'ter'in accordance with the dialed-code, means at a receiving station to translate received radio waves into ringing currents, means for translating the ringing currents'intothe code number, a selector switchatthe receivingstation controlled by saidineans, means to advance said selector switch off norma'lin response to each digit, means to bring said selector switch to normal between digits, selecting Jrelays, one corresponding to each selectivedigitof the code number, meansto successively operate the selecting relaysin response to the successive operation of the selector switch, and a signaling circuit com- ?pleted onlynpon the successive operation of said relays in response to the code for the selected station.

normal between i digits, a plurality of select- 7. In a radio telephone system, means for selectively signaling a desired station comprisin means for transmitting the codenumber of the station in the form of successive digits, a radio transmitter, means to apply ringing current to said radio transmitter in accordance with the dialed code, means at a receiving station to translate received radio waves into ringing currents, means for translating the ringing currents into the code number, a selector switch at the receiving station controlled by'said means, means to advance said selector switch off normal in response to-each digit,means to bring said selector switch to normal between'digits,selecting relays, one corresponding to each selecting digit of the code number, means whereby the operation of the selector switch in response to the first selective digit will actuate one of said relays only if said digit-is the plurality of receiving stations 'to translate received radio waves into ringing cur-rents,

aneans at said stations ttor translating the ring ng currents into the code number, "a

selector switch at each receiving stationoontrolled bysaid means, means to advancesaid selector switch off normal in response to each digit, aneans to bring said selector switch to in'g relays :at each receiving "station, one corresponding to eao'hsc'leo'tive digit-of a eodc number, means responsive to the first digit to brin g the selector switches at all receiving stations and their assoc ated apparatus to normal, means responsive to the second digit to actuate the selector switch-at each receiving station and complete the circuit of p 'T the selective relay thereat 1 only if the digit corresponds to a digit ofthecode number of :the station, i'neans to actuate the other selecting relays at each receiving station in to complete a signaling circuit under the control of said selecting relays at the desired station.

9. Ina signaling system, 'meens' for' selecringing cur-rent to saidtransinitter' in ace cordance with the dialed code, means at -a tively signaling a desired station comprising means for transmitting the code number of the station in the form of successive digits, means at the receiving station for receiving the code number, a selector switch at the receiving station controlled by said means, said switch being arranged to be operated in one direction only so that when advanced from its normal position it may thereafter be brought to normal by being further advanced, means to advance said selector switch off normal in response to each digit, means to further advance said selector switch to normal between digits, a signaling circuit, and means actuated to complete said circuit by successively advancing the selector switch in response only to each digit of the code of that station.

10. In a signaling system, means for selectively signaling a desired station comprising means for transmitting the code number of the station in the form of successive digits, means at a receiving station for receiving the code number, a selector switch at the receiving station controlled by said means, said switch being arranged to be operated in one direction only so that when advanced from its normal position it may thereafter be brought to normal by being further advanced, means to advance said selector switch ofi normal in response to each digit, means to further advance said selector switch to normal between digits, selecting relays, one corresponding to each selective digit of the code number, means to successively operate the selecting relays in response to the successive operation of the selector switch, and a signaling circuit completed only upon the successive operation of said relays in response to the code for the selected station.

11. In a signaling system, means for selectively signaling a desired station com prising means for transmitting the code number of the station in the form of successive digits, means at a receiving station for receiving the code number, a selector switch at the receiving station controlled by said means, said switch being arranged to be operated in one direction only so thatselector switch to normal between digits, selecting relays, one correspondin to the selective digit of the code number, means whereby the operation of the selector switch in response to the first selective digit will actuate one of said relays only if said digit is the first selective digit of the code number of that station, means whereby the successive actuation of the selector switch in response to additional digits will actuate the remaining.relays only when the digits received correspond to the digits of the code number of the station, and a signaling circuit controlled by said selecting relays.

12. In a signaling system, a transmitting station and a pluralityof receiving stations, means at said transmitting station for selectively signaling a desired receiving station, said means comprising means for transmitting the code number of the station in the form of successive digits, means at the receiving stations for receiving the code number, a selector switch at each receiving station controlled by said means, said switch being arranged to be operated in one direction only so that when advanced from its normal position it may thereafter be brought to normal by being further advanced, means to advance said selector switch ofi normal in response to each digit, means to further advance said selector switch to normal between digits, a plurality of selecting relays at each receiving station, one corresponding to each selective digit of a code number, means responsive to the first digit to bring the selector switches at all the receiving stations and their associated apparatus to normal, means responsive to the second digit to actuate the selector switch at each receiving station and complete the circuit of the selecting relay thereat only if the digit corresponds to a digit of the code number of the station, means to actuate the other selecting relays at each receiving station in response to the successive actuation of the selector switch of each station only when the selective digits actuating the switch correspond to the remaining digits of the code number of the particular station, and means to complete the signaling circuit under the control of said selecting relays at the desired station.

,In testimony whereof I have signed my name to this specification this 17th day of May, 1924.

MILTON L. ALMQUIST. 

